Depends on the upgrade model.
For those that require a factory rework, it might make sense if you lived near the manufacturer and it isn't expensive to ship to and from the manufacturer .
Others have dealer fitted upgrades like Bel Canto. I have a Bel Canto DAC3.5VB that I have upgraded from Mk I to Mk II specs and I recall Bel Canto offered upgrades for the DAC3 to DAC3VB and then a DAC3.x upgrade which fitted in 3.5 components. That was easy enough to do without a hefty shipping bill.
I think Wyred4Sound said their DAC2 was upgradeable too but I don't recall any upgrades being offered as yet.
If shipping is expensive (especially including insurance etc), most just trade the gear in for a new model :)
For those that require a factory rework, it might make sense if you lived near the manufacturer and it isn't expensive to ship to and from the manufacturer .
Others have dealer fitted upgrades like Bel Canto. I have a Bel Canto DAC3.5VB that I have upgraded from Mk I to Mk II specs and I recall Bel Canto offered upgrades for the DAC3 to DAC3VB and then a DAC3.x upgrade which fitted in 3.5 components. That was easy enough to do without a hefty shipping bill.
I think Wyred4Sound said their DAC2 was upgradeable too but I don't recall any upgrades being offered as yet.
If shipping is expensive (especially including insurance etc), most just trade the gear in for a new model :)